The present invention relates generally to a system and method for removing solid debris from completion fluids being pumped through a surface drilling rig circulation system prior to flowing downhole.
In the prior art, when debris is pumped or introduced downhole, such debris or trash becomes lodged in downhole equipment or production tools and impairs their performance or causes failure. Free floating debris such as drilling mud solids, paint chips, pipe dope, metal shavings, rust shale, fibers and other associated debris are typically found in the completion fluids. Accumulation of this collective array of debris will lead to equipment failure as previously noted.
As shown in FIG. 1, prior art workover systems typically comprise first and second settling tanks 2 and 3, a low pressure pump 4, a low pressure filter 5, and a high pressure pump 6. The low pressure pump 4 and low pressure filter 5 transport and purify the workover fluid from settling tank 2 to settling tank 3. A high pressure pump 6 draws workover fluid from settling tank 3 for insertion into the well Christmas tree 8 located at the top of the wellbore casing 7. A high pressure conduit 10 extends from the high pressure pump 6 to the Christmas tree 8. The systems further comprise a return conduit 9 which extends from the Christmas tree 8 to the first settling tank 2. Relatively dirty completion fluid is drawn from the Christmas tree and pumped into the first settling tank 2, where the bulk of the debris settles out of the fluid. Completion fluid is then pumped out of the top of the first settling tank 2 so as to withdraw as little of the debris as possible with the completion fluid. As the completion fluid is withdrawn from the first settling tank 2, it is filtered by the low pressure filter 5 to remove any debris suspended in the completion fluid. This filtered completion fluid is pumped into the second settling tank 3 to allow any remaining debris to settle out of the fluid.
Low pressure filtration systems for implementation between the first and second settling tanks 2 and 3 are known. For example, U.S. Pat. No. 4,352,739, incorporated herein by reference, discloses a liquid cleaning system for liquid that is substantially continuously circulated and which becomes contaminated with solid particulate and debris during circulation. The liquid cleaning system, which is particularly advantageous to cleaning liquid that is circulated within a petroleum wellbore during completion and workover activities, incorporates a vibratory screen separator for accomplishing preliminary separation of large particulate and debris from the contaminated liquid and which also incorporates a filtration bank having a plurality of filters that are each interconnected with inlet discharge and drain headers. The filter bank incorporates a valving system having the capability of accomplishing backflushing by circulating clean fluid in reverse manner through selected ones of the filters to remove collected solid particulate therefrom and transport the removed particulate to the drain header.
Similarly, U.S. Pat. No. 4,560,483, incorporated herein by reference, discloses a filtering system using at least two filter vessels with a plurality of filter elements having absolute filtration capability. The filter elements use a nominal filter of diatomaceous earth or a perlite filter and a precoat layer, an outer wire layer, an absolute filter layer, a fine wire layer, a course wire layer, and a tube core for receiving filter flow therein. A pump is provided for injecting a predetermined amount of filter aid to a precoat tank containing clean fluid. The slurry of filter aid and clean fluid is then pumped into one of the filter vessels for precoating the filter elements. The unfiltered fluid is then allowed to enter the vessel and to be filtered through the filtering elements while virgin filter aid is continuously injected into the unfiltered fluids prior to the fluids entering the filter vessel. This apparatus is used for filtering completion and workover fluids utilized during oil and gas well drilling and completion operations.
Another example is found in U.S. Pat. No. 4,456,061, incorporated herein by reference. This patent discloses well cleaning circulation fluids and production or workover processes. In particular, a cylindrical housing is adapted to receive and discharge fluid in a subterranean well. In a preferred form, a plate is positioned in the cylinder separating it into first and second chambers. Filter adapter receiving means are disposed across the plate, with a filter adapter securable therein, the adapter having a passageway extending to the chambers. The adapter has a cylindrical housing having an enlarged cartridge positioning portion. A grooveway is defined on the adapter extending exteriorly therearound for securing one end of a secondary cartridge filter. A secondary cartridge filter has an inner filter completely surrounded by a replaceable and reuseable primary sleeve filter and is positionable on the adapter, the filter providing a seal having an interiorly facing circumferentially extending lip for contact with the exterior of the cylindrical housing when the filter is located on the adapter, for sealingly securing the filter to the adapter.
While many filter systems are known throughout the industry for filtering the circulation fluid in the settling tanks, these systems are not completely effective in removing debris from the completion fluid as the fluid is pumped into the wellbore. In particular, because the settling tanks are sometimes located several hundred feet away from the well being worked over, the high pressure conduit 10 can retain a fair amount of debris which is carried by the completion fluid into the well. Therefore, there is a need for a filtration system and method which more effectively removes debris and particulates from the completion fluid prior to the fluid being introduced into the well.
To satisfy this need in the well completion fluid circulation field, a high pressure filtration system is placed in the high pressure conduit immediately upstream from the Christmas tree. This high pressure filtration system cleans fine particulates and debris from the circulation fluid as high volumes of circulation fluid rapidly pass through the filtration system under high pressure.
According to one aspect of the invention, there is provided a fluid filtration system of well workover fluids, the system comprising: a first settling tank which stores fluid; a second settling tank which stores fluid; a low pressure pump in fluid communication with the first and second settling tanks; a low pressure filter in fluid communication with the first and second settling tanks; a high pressure pump in fluid communication with the second settling tank; and a high pressure filter in fluid communication with the second settling tank, wherein the high pressure filter comprises: an inlet; an outlet; a plurality of input feed lines in fluid communication with the inlet; a plurality of output feed lines in fluid communication with the outlet; a plurality of filter canisters, wherein at least one filter canister is in fluid communication with each input feed line and each output feed line.
According to a further aspect of the invention, there is provided an in-line, high-pressure, fluid filter of well workover fluids, the filter comprising: an inlet; an outlet; and a high pressure filter canister in fluid communication with the inlet and the outlet, the filter canister comprising a perforated base pipe and a media screen.
According to still anther aspect of the invention, there is provided a high pressure fluid filter of well workover fluids, the filter comprising: an inlet; an outlet; and a high pressure filter canister in fluid communication with the inlet and the outlet, the filter canister comprising a perforated base pipe and a media screen; a plurality of input feed lines in fluid communication with the inlet; a plurality of output feed lines in fluid communication with the outlet; and a plurality of high pressure filter canisters, wherein at least one filter canister is in fluid communication with each input feed line and each output feed line.
According to another aspect of the invention, there is provided a process for filtering fluid for circulation in a well, the process comprising: standing the fluid a first time, whereby debris in the fluid is allowed to settle; filtering under a first pressure the fluid of the standing the fluid a first time, whereby further debris is removed from the fluid; standing the fluid a second time, whereby further debris is allowed to settle; and filtering the fluid of the standing the fluid a second time under second pressure, wherein the second pressure is higher than the first pressure, whereby further debris is removed from the fluid.
The high pressure filter of the present invention withstands high working pressures and also withstands high velocity erosion associated with high debris loading. Debris such as barite from drilling mud, frac sand or bauxite pumped at high rates could erode or wear a hole in the metal filter canisters leading to plugged or serious reduction of hydrocarbon formations with the producing reservoir.